The nervous system comprises the central and the peripheral nervous system. The central nervous system (CNS) is composed of the brain and spinal cord; the peripheral nervous system (PUS) consists of all of the other neural elements, namely the nerves and ganglia outside of the brain and spinal cord.
Damage to the nervous system may result from a traumatic injury, such as penetrating trauma or blunt trauma, or a disease or disorder, including but not limited to Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis (ALS), diabetic neuropathy, senile dementia, and ischemia.
Maintenance of central nervous system integrity is a complex “balancing act” in which compromises are struck with the immune system. In most tissues, the immune system plays an essential part in protection, repair, and healing. In the central nervous system, because of its unique immune privilege, immunological reactions are relatively limited (Streilein, 1993, 1995). A growing body of evidence indicates that the failure of the mammalian central nervous system to achieve functional recovery after injury is a reflection of an ineffective dialog between the damaged tissue and the immune system. For example, the restricted communication between the central nervous system and blood-borne macrophages affects the capacity of axotomized axons to regrow; transplants of activated macrophages can promote central nervous system regrowth (Lazarov Spiegler et al, 1996; Rapalino et al, 1998).
Activated T cells have been shown to enter the central nervous system parenchyma, irrespective of their antigen specificity, but only T cells capable of reacting with a central nervous system antigen seem to persist there (Hickey et al, 1991; Werkele, 1993; Kramer et al, 1995). T cells reactive to antigens of central nervous system white matter, such as myelin basic protein (MBP), can induce the paralytic disease experimental autoimmune encephalomyelitis (EAE) within several days of their inoculation into naive recipient rats (Ben-Nun, 1981a). Anti-MBP T cells may also be involved in the human disease multiple sclerosis (Ota, K. et al, 1990; Martin, 1997). However, despite their pathogenic potential, anti-MBP T cell clones are present in the immune systems of healthy subjects (Burns, 1983; Pette, M. et al, 1990; Martin et al, 1990; Schluesener et al, 1985). Activated T cells, which normally patrol the intact central nervous system, transiently accumulate at sites of central nervous system white matter lesions (Hirschberg et al, 1998).
A catastrophic consequence of central nervous system injury is that the primary damage is often compounded by the gradual secondary loss of adjacent neurons that apparently were undamaged, or only marginally damaged, by the initial injury (Faden et al, 1992; Faden 1993; McIntosh, 1993). The primary lesion causes changes in extracellular ion concentrations, elevation of amounts of free radicals, release of neurotransmitters, depletion of growth factors, and local inflammation. These changes trigger a cascade of destructive events in the adjacent neurons that initially escaped the primary injury (Lynch et al, 1994; Bazan et al, 1995; Wu et al, 1994). This secondary damage is mediated by activation of voltage-dependent or agonist-gated channels, ion leaks, activation of calcium-dependent enzymes such as proteases, lipases and nucleases, mitochondrial dysfunction and energy depletion, culminating in neuronal cell death (Yoshina et al, 1991; Hovda et al, 1991; Zivin et al, 1991; Yoles et al, 1992). The widespread loss of neurons beyond the loss caused directly by the primary injury has been called “secondary degeneration.”
One of the most common mediators which cause self-propagation of the diseases even when the primary risk factor is removed or attenuated is glutamate, an excitatory amino acid capable of displaying dual activity: playing a pivotal role in normal central nervous system (CNS) functioning as an essential neurotransmitter, but becoming toxic when its physiological levels are exceeded. Elevation of glutamate has been reported in many CNS disorders. In its role as an excitotoxic compound, glutamate is one of the most common mediators of toxicity in acute and chronic (including optic nerve degeneration in glaucoma) degenerative disorders (Pitt et al., 2000 and Schoepp et al., 1996). Endogenous glutamate has been attributed to the brain damage occurring acutely after status epilepticus, cerebral ischemia or traumatic brain injury. It may also contribute to chronic neurodegeneration in such disorders as amyotrophic lateral sclerosis and Huntington's chorea.
Intensive research has been devoted to attenuating the cytotoxic effect of glutamate by the use of locally acting drugs, such as NMDA-receptor antagonists (Brauner-Osborne et al., 2000). Conventional therapy of this type is often unsatisfactory, however, as in neutralizing the toxic effect it is likely to interfere with the physiological functioning. In humans, such compounds have psychotropic and other side effects that make them unsuitable as therapeutic agents. They also have the disadvantage of interfering with the essential physiological functioning of glutamate as a ubiquitous CNS neurotransmitter. Because glutamate activity is essential for normal physiological functioning, yet is potentially devastating after acute injury or in chronic CNS disorders, any attempt to neutralize its harmful effect must do so without eliminating its essential activity at other sites in the body.
Another tragic consequence of central nervous system injury is that neurons in the mammalian central nervous system do not undergo spontaneous regeneration following an injury. Thus, a central nervous system injury causes permanent impairment of motor and sensory functions.
Spinal cord lesions, regardless of the severity of the injury, initially result in a complete functional paralysis known as spinal shock. Some spontaneous recovery from spinal shock may be observed, starting a few days after the injury and tapering off within three to four weeks. The less severe the insult, the better the functional outcome. The extent of recovery is a function of the amount of undamaged tissue minus the loss due to secondary degeneration. Recovery from injury would be improved by neuroprotective treatment that could reduce secondary degeneration. For example, alleviation of the effect of glutamate is a frequent target of neuroprotective drug development. Among the drugs which are being developed for this purpose are N-methyl-D-aspartate (NMDA)-receptor or alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)-receptor antagonists. These drugs will inevitably have severe side effects as they interfere with the functioning of NMDA and AMPA receptors, which are crucial for CNS activity. One of the most intensely studied NMDA-receptor antagonists is MK801, which provides effective neuroprotection but with severe side effects. In animal models of cerebral ischemia and traumatic brain injury, NMDA and AMPA receptor antagonists protect against acute brain damage and delayed behavioral deficits. Such compounds are undergoing testing in humans, but therapeutic efficacy has yet to be established. Other clinical conditions that may respond to drugs acting on glutamatergic transmission include epilepsy, amnesia, anxiety, hyperalgesia and psychosis (Meldrum, 2000).
In the laboratory of the present inventors, it has recently been discovered that activated T cells that recognize an antigen of the nervous system (NS) of the patient promote nerve regeneration or confer neuroprotection. Reference is made to PCT publication WO 99/60021, the entire contents of which is hereby incorporated herein by reference. More specifically, T cells reactive to MBP were shown to be neuroprotective in rat models of partially crushed optic nerve (Moalem et al, 1999) and of spinal cord injury (Hauben et al, 2000). Until recently, it had been thought that the immune system excluded immune cells from participating in nervous system repair. It was quite surprising to discover that NS-specific activated T cells could be used to promote nerve regeneration or to protect nervous system tissue from secondary degeneration which may follow damage caused by injury or disease of the CNS or PNS.
NS-specific activated T cells as described in said Wo 99/60021 publication are activated T cells having specificity for an antigen of the NS of a patient. The antigen used to confer the specificity to the T cells may be a self NS-antigen of the patient, a peptide derived therefrom, or an NS-antigen of another individual or even another species, or a peptide derived therefrom, as long as the activated T cell recognizes an antigen in the NS of the patient.
Said NS-specific activated T cells are for use to promote nerve regeneration or to prevent or inhibit the effects of disease. If the disease being treated is an autoimmune disease, in which the autoimmune antigen is an NS antigen, the T cells which are used for the treatment of neural damage or degeneration caused by such disease are not activated against the same autoimmune antigen involved in the disease.
The above-referenced PCT publication WO 99/60021 discloses that therapy for amelioration of effects of injury or disease comprising administration of NS-specific activated T cells may optionally be in combination with an NS-specific antigen or peptide derived therefrom. An NS-specific antigen as defined in said WO 99/60021 refers to an antigen that specifically activates T cells such that following activation, the activated T cells accumulate at a site of injury or disease in the NS of the patient. Furthermore, oral administration of NS-specific antigen or a peptide derived therefrom can be combined with active immunization to build up a critical T cell response immediately after injury.
In this prior invention, the NS-specific antigen used to activate the T cells in vitro or in vivo or to immunize the patient, may be an antigen obtained from NS tissue, preferably from tissue at a site of CNS injury or disease. Natural or synthetic NS-specific antigens or epitopes were disclosed to include MBP, MOG, PLP, MAG, S-100, β-amyloid, Thy-1, P0, P2 and a neurotransmitter receptor. Specific illustrative examples of such useful NS-specific antigens disclosed in WO 99/60021 are human MBP, human proteolipid protein (PLP), and human oligodendrocyte glycoprotein. Also disclosed were peptides derived from NS-specific, self-antigens or derivatives of NS-specific antigens that activate T cells, but do not induce an autoimmune disease, such as a peptide comprising amino acids 51-70 of myelin basic protein (MBP).
The mechanism of action of such NS-specific T cells has yet to be discovered, but the massive accumulation of exogenously administered T cells at the site of CNS injury suggests that the presence of T cells at the site of injury plays a prominent role in neuroprotection. It appears, however, that the accumulation, though a necessary condition, is not sufficient for the purpose, as T cells specific to the non-self antigen ovalbumin also accumulate at the site, but have no neuroprotective effect (Hirschberg et al, 1998).
A high molecular weight synthetic basic random copolymer consisting of L-Ala, L-Glu, L-Lys and L-Tyr residues in the molar ratio of about 6 parts Ala to 2 parts Glu to 4.5 parts Lys to 1 part Tyr, and having a molecular weight of 15,000-25,000, was first described in U.S. Pat. No. 3,849,550 as an agent for treatment or prevention of experimental allergic encephalomyelitis (EAE), a disease resembling multiple sclerosis (MS) that can be induced in susceptible animals. Batches of this copolymer of average molecular weight 23,000, designated Copolymer 1 or Cop 1, were shown to be highly effective in protecting and suppressing EAE in several animal species (Teitelbaum et al, 1971, 1974a, 1974b).
Later, Cop 1 was found to significantly reduce the number of relapses in patients with the exacerbating-remitting form of MS (Bornstein et al, 1990; Sela et al, 1990; Johnson et al, 1994). Copolymer 1, in the form of the acetate salts of synthetic polypeptides containing L-Glu, L-Ala, L-Tyr and L-Lys with an average molar fraction of 0.141, 0.427, 0.095 and 0.338, is the active ingredient of COPAXONE®, a medicament for the treatment of multiple sclerosis.
It is thus apparent that the effect of Copolymer 1 in the treatment of MS is in in the achievement of suppression or deactivation of autoimmune T cell reactivity to myelin antigens in multiple sclerosis patients. For this purpose, Copolymer 1 is administered without adjuvants by daily subcutaneous injection.
Cop 1 was originally designed to mimic MBP and to induce EAE, but was found to be non-encephalitogenic and even to suppress EAE induced by MBP (Teitelbaum et al, 1971) (PLP) (Teitelbaum et al, 1996), or (MOG) (Ben-Nun et al, 1996). The precise mechanisms by which Cop 1 prevents the development of EAE and ameliorates multiple sclerosis (MS) are not yet known. Nevertheless, some important immunological properties of this copolymer have emerged. Studies have demonstrated partial cross-reactivity of Cop 1 with MBP at both the T cell (Webb et al, 1973) and the antibody (Teitelbaum et al, 1988) level. Cop 1 can serve as an antagonist of the T-cell antigen receptor for the MBP immunodominant epitope (Aharoni, 1998). It can also bind to various MHC class II molecules and prevent them from binding to T cells with specific antigen-recognition properties (Fridkis-Hareli et al, 1999a). In rodents, Cop 0.1 induces regulatory cells that probably act as bystander suppressors (Aharoni, 1998) of encephalitogenic T cells. Adoptive transfer of such T cells was found to prevent the development of EAE induced by MBP (Aharoni et al, 1993), PLP (Aharoni, 1998), or whole spinal cord homogenate (Aharoni et al, 1997).
Furthermore, direct evidence has also been reported both for competitive interaction of Cop 1 and related copolymers and Collagen II (CII) peptide with rheumatoid arthritis (RA)-associated HLA-DR molecules and for inhibition of CII-specific T cell responses, suggesting that these compounds may be effective against rheumatoid arthritis (Fridkis-Hareli, 1998, 1999b).
Oral administration of autoantigen in order to obtain “oral tolerance” has been disclosed for the treatment of various autoimmune diseases. For example, EP 359 783 discloses the oral administration of MBP for the treatment of multiple sclerosis. PCT International Publications WO 91/12816, WO 91/08760 and WO 92/06704 all disclose the treatment of other autoimmune diseases using the oral tolerance method with a variety of autoantigens. Treatment of multiple sclerosis by ingestion or inhalation of Copolymer 1, to achieve suppression of the autoimmune T cell response to, myelin antigens, has been disclosed in PCT publication WO 9B/30227.
Compounds related to Copolymer 1 have also been studied and found to have properties similar to Copolymer 1. For example, copolymers composed of three of the four amino acids found in Copolymer 1 bind to purified Class II MHC molecules (Fridkis-Hareli et al, 1999a, WO 005250). In addition, binding motifs of Copolymer 1 to multiple sclerosis- and rheumatoid arthritis-associated HLA-DR molecules have recently been elucidated (Fridkis-Hareli et al, 1999b). From these binding motifs, polypeptides of fixed sequence can readily be proposed and tested for binding to the peptide binding groove of the HLA-DR molecules. Such peptides would be expected to act in a way similar to Cop 1 itself. Examples of such synthetic peptides are disclosed in WO 005249.
Citation or identification of any reference in this section or any other part of this application shall not be construed as an admission that such reference is available as prior art to the invention.